1. Field of the Invention
This invention relates to electron microscopy and more particularly to the computer control of the tilting of the sample stage in transmission electron microscopes to enable the sample stage to be tilted along two perpendicular axes to re-orientate the sample without using diffraction mode.
2. Related Art
U.S. Pat. No. 3,727,051 discloses a control system with an electrical computing circuit for sensing tilting and the position of the point under observation to adjust the specimen stage in an electron microscope.
Electron microscopes, including transmission-electron microscopes (TEM) and scanning electron microscopes (SEM) have become one of the most important instruments in determining the microstructure of material. Unfortunately electron microscopes are difficult to operate and require significant operator experience and skill to obtain satisfactory information. A significant factor in the operation of an electron microscope is the proper tilting of the sample, as even experienced operators cannot be certain that optimum conditions exist when making an observation because of the many possible orientations of the sample.
Moreover, in known tilting systems, when the sample is tilted the operator needs to observe the diffraction pattern of the sample, which means that the image of the sample cannot be observed at the same time. Consequently, if the spot of interest of the sample moves off the image screen during tilting the spot of interest may be temporarily lost. Furthermore, when using a double tilt stage (the sample can be tilted in two perpendicular directions) the operator needs to switch back and forth between the diffraction mode and the image mode to make sure that the spot of interest remains in view with tilting of the sample. Even for experienced operators it is very difficult to maintain the spot within the screen area when tilting the sample stage for very small grain-sized polycrystalline samples or with samples containing more than one phase.